1. Field of the Invention
The present invention relates to a rotational angle sensing device.
2. Description of Related Art
In a prior art rotational angle sensing device, which senses a rotational angle of an accelerator pedal, two magnets are opposed to each other about a central axis and are fixed at the accelerator pedal, which is rotatable forward or backward depending on a pedal force applied from a driver of a vehicle to the accelerator pedal. A Hall IC is placed at the central axis such that the two magnets are rotatable relative to the Hall IC. A voltage signal, which is outputted from the Hall IC, is sensed to sense a rotational angle of the accelerator pedal. Japanese Unexamined Patent Publication No. 2007-132819A (corresponding to US2007/0103149A1) teaches such a rotational angle sensing device. Specifically, in the rotational angle sensing device, a cylindrical yoke, which has a circular cross section, is placed radially outward of the magnets to form a magnetic circuit, thereby increasing a density of a magnetic flux between the magnets.
In this type of rotational angle sensing device, volumes of the magnets have a large influence on the manufacturing costs. Therefore, it is conceivable to reduce the volumes of the magnets to reduce the manufacturing costs.
However, when the volumes of the magnets are reduced, a magnetic flux, which is indicated by an arrow φ100 in FIG. 7, flows between circumferential ends of the magnets 101, 102 and an inner wall of the yoke 103. This may possibly reduce a range of a parallel magnetic field, in which the magnetic flux flows in parallel between the magnets 101, 102. Therefore, when the Hall IC 104 is displaced from the central axis of the yoke 103 due to, for example, presence of a manufacturing tolerance, a voltage signal, which is outputted from the Hall IC 104, may possibly change to reduce a sensing accuracy.